RESUMEN
Identification of mass-spectrum peaks is an indispensable step of an atom-probe tomography reconstruction process and can be a time-consuming procedure, vulnerable to errors, if performed manually. We propose a Bayesian approach to the peak identification problem, based on ranking of candidate ions according to their calculated posterior probabilities. The sample model is reconstructed by iteratively accepting top-ranked ions while taking into account prior information, models of experimental errors, and the already accepted ions. The designed approach has been applied to a number of time-of-flight mass spectra, measured for inorganic samples, and enabled a reliable construction of sample models, consistent with the results of manual analysis. Additionally, a "sliding window" approach for an accurate and efficient peak decomposition of a mass spectrum was established on the base of Fisher information.
RESUMEN
A general theoretical approach to the description of epitaxial layers with essentially different cell parameters and in-plane relaxation anisotropy has been developed. A covariant description of relaxation in such structures has been introduced. An iteration method for evaluation of these parameters on the basis of the diffraction data set has been worked out together with error analysis and reliability checking. The validity of the presented theoretical approaches has been proved with a-ZnO on r-sapphire samples grown in the temperature range from 573â K up to 1073â K. A covariant description of relaxation anisotropy for these samples has been estimated with data measured for different directions of the diffraction plane relative to the sample surface.
RESUMEN
A novel method for the calculation of the X-ray susceptibility of a crystal in a wide range of radiation wavelengths is described. An analytical interpolation of one-electron wave functions is built to approximate the solution to Hartree-Fock equations for all atoms and ions of the periodic system of elements with high accuracy. These functions allow the calculation of the atomic form factors in the entire range of a transmitted momentum as well as the description of their anisotropy taking into account external and intracrystalline fields. Also, an analytical approximation for the force matrix of an arbitrary crystal is obtained and the microscopic calculation of the Debye-Waller factor for crystals with a complicated unit cell is presented.
RESUMEN
The intensity of coherent X-radiation (CXR) from a relativistic electron beam interacting with the crystal [Feranchuk, Ulyanenkov, Harada & Spence (2000). Phys. Rev. E, 62, 4225-4234] is studied in view of its application to the phase determination problem. The analysis of CXR spectra is shown to permit an independent measurement of unit-cell structure factors, defined by both the electron-density distribution and the nucleus positions. In relation to these structure factors, two new types of Patterson function are introduced that can simplify the solution of crystal structure.
RESUMEN
A theoretical analysis of radiation spectra produced during the coherent interaction of nonrelativistic electrons with crystals has been carried out. The output intensity has been found to be the result of interference between two distinguishable phenomena, coherent Bremsstrahlung and parametric x-ray radiation. The latter is determined by a coherent summation of transition radiation from electrons interacting with successive crystallographic planes. The interference is shown to be considerable for the case of nonrelativistic electrons, and so allows us to describe quantitatively the experiments of Korobochko et al. (Zh. Eksp. Teor. Fiz. 48, 1248 (1965) [Sov. Phys. JETP 21, 834 (1965)]) and Reese et al. [Philos. Mag. A 49, 697 (1984)]. The conditions for possible application of coherent x-ray radiation, a comparison with synchrotron radiation, and the requirements for experimental setup are discussed.
RESUMEN
A theoretical analysis of the parametric X-radiation (PXR) produced by the nonrelativistic electrons in an X-ray tube with a monocrystalline anode is presented. It is shown that PXR can be considered as a source of quasi-monochromatic X-radiation for laboratory dif-fraction experiments. The intensity of the PXR is comparable with the intensity of the characteristic radiation, but the frequency of the former can be varied in a wide range. Possible applications of the phenomenon for crystallography are discussed.